Transistor(part-1)

Blog Number:- 008
Hello Everybody,
I hope you all will be fine.

Today we are going to discuss about Transistor.

Transistor:-

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power.

     It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal.

         The essential usefulness of a transistor comes from its ability to use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals. This property is called gain. It can produce a stronger output signal, a voltage or current, which is proportional to a weaker input signal; that is, it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements.

There are two types of transistors, which have slight differences in how they are used in a circuit. A bipolar transistor has terminals labeled base, collector, and emitter. A small current at the base terminal (that is, flowing between the base and the emitter) can control or switch a much larger current between the collector and emitter terminals. For a field-effect transistor, the terminals are labeled gate, source, and drain, and a voltage at the gate can control a current between source and drain.

Silicon Sandwich to make Transistor

      Suppose we join a piece of n-type silicon to a piece of p-type silicon and put electrical contacts on either side. Exciting and useful things start to happen at the junction between the two materials. If we turn on the current, we can make electrons flow through the junction from  the n-type side to the p-type side and out through the circuit. This happens because the lack of electrons on the p-type side of the junction pulls electrons over from the n-type side and vice-versa. But if we reverse the current, the electrons won't flow at all. What we've made here is called a diode (or rectifier). It's an electronic component that lets current flow through it in only one direction. It's useful if you want to turn alternating (two-way) electric current into direct (one-way) current.

      Now suppose we use three layers of silicon in our sandwich instead of two. We can either make a p-n-p sandwich (with a slice of n-type silicon as the filling between two slices of p-type) or an n-p-n sandwich (with the p-type in between the two slabs of n-type). If we join electrical contacts to all three layers of the sandwich, we can make a component that will either amplify a current or switch it on or off—in other words, a transistor.

Symbolic Representation of Transistors

Transistor as Diode

So, that's all for this Session. In the next session we will proceed with discussion on BJT-Configuration and several relation between the three terminals,  and Transistor as switch.

If you have any query related to topic, feel free to comment.

Thank you.